In the field of medical analyses, to ascertain pathological states defined as inflammatory, the speed of sedimentation of the corpuscular part of the blood is measured, particularly the erythrocytes or red cells.
To establish the ESR, various methods have been adapted but these have not proved to be completely satisfactory, in that detection is neither quick nor practical.
In these methods, which use different measuring systems, the blood taken from the patients is put into tubular containers and subsequently, possibly after centrifuging, the due measurements are made on the blood samples.
Other systems provide to detect, at pre-set intervals of time, the position of the separation interface between the fluid plasma part of the blood, substantially clear, and the corpuscular part consisting of red and white cells and platelets, which is more turbid.
Other systems provide to detect the optical density or absorbance of the blood in correspondence with the separation interface.
Other cases provide to use optothermic sensors suitable to detect at defined intervals the heat produced by the blood sample absorbing radiation which strikes it.
The different methods to determine ESR which have been proposed until now are all characterized by an initial dead time which has a considerable influence on the time required for analysis; the latter cannot therefore be done in succession with other analyses which are much quicker, such as for example blood cell counts.
Conventional methods, moreover, have to use disposable containers, which entails an increase in costs both to purchase them and to dispose of them. Furthermore, the quantity of blood needed to do the analysis is high, and this entails problems in some particular cases, for example when the analysis involves children.
The state of the art also includes a method, proposed by the same Applicant, which provides to withdraw the blood to be analyzed from the container in which it is kept and to introduce the blood into a measuring volume, of limited thickness, which is used for various measurements made on different samples.
This method is based on the detection of the optical density or absorbance of the blood at a fixed point of the measuring volume, which is made to rotate to accelerate the sedimentation of the blood.
The means used to detect the absorbance comprise devices to emit/detect electromagnetic radiations associated with the measuring volume. The absorbance values detected are directly proportional to the number of cells in the blood sample at the point of observation, and this number varies over time due to the effect of the sedimentation of the cells.
By studying the absorbance over time it is possible to obtain the ESR value by eliminating the initial dead times and obviating the need to use disposable containers for the analysis.
Moreover, the quantity of blood needed is less and therefore the analysis can be done without any problems, even on paediatric patients.
Although it has these advantages, the method is also characterized by some problems which prevent it from being used in a completely satisfactory manner.
The size of the apparatus used to measure the ESR and the difficulties involved in managing several centrifugal means limit the possibility of using the system with an integrated instrument for counting the blood cells. Moreover, the size of the apparatus requires the analyses to be made in the laboratory and the method of analysis itself still requires volumes of blood which are in any case considerable.
Furthermore, after every measurement, the centrifugal means and the volume associated therewith always have to be repositioned with respect to the emission/detection means, which creates problems and anomalies in controlling the flow of blood.
In this apparatus, after each test, the blood sample is discharged and a new blood sample is introduced into the measuring volume.
To avoid washing the measuring volume after discharge, the residue of the sample which has already been analyzed is discharged by the new blood sample to be analyzed, since the hydraulic path which the blood has to follow to avoid pollution is rather long; this increases the volume of blood which has to be used.
A further limit of this method is that the acquisition of the photometric data depends on the speed of rotation of the measuring volume and therefore cannot be considered a continuous phenomenon.
The Applicant has devised and embodied this invention to perfect and extend the field of use of the apparatus described above, and also to obtain further advantages.